In the printing field, the impact type printer has been the predominant apparatus for providing increased throughput of printed information. The impact printers have included the dot matrix type wherein individual print wires are driven from a home position to a printing position by individual and separate drivers. The impact printers also have included the full character type wherein individual type elements are caused to be driven against a ribbon and paper or like record media adjacent and in contact with a platen.
The typical and well-known arrangement in a printing operation provides for transfer of a portion of the ink from the ribbon to result in a mark or image on the paper. Another arrangement includes the use of carbonless paper wherein the impact from a print wire or a type element causes rupture of encapsulated material for marking the paper. Also known are printing inks which contain magnetic particles wherein certain of the particles are transferred to the record media for encoding characters in manner and fashion so as to be machine readable in a subsequent operation. One of the known encoding systems is MICR (Magnetic Ink Character Recognition) utilizing the manner of operation as just mentioned.
While the impact printing method has dominated the industry, one disadvantage of this type of printing is the noise level which is attained during printing operation. Many efforts have been made to reduce the high noise levels by use of sound absorbing or cushioning materials or by isolating the printing apparatus.
More recently, the advent of thermal printing which effectively and significantly reduces the noise levels has brought about the requirements for heating of extremely precise areas of the record media by use of relatively high currents. The intense heating of the localized areas causes transfer of ink from a ribbon onto the paper or like receiving media. Alternatively, the paper may be of the thermal type which includes materials that are responsive to the generated heat.
The use of thermal transfer printing, especially when printing in a serial manner, can result in ribbon offset to unprinted areas of the receiving substrate. Ribbon offset is a term used to describe the unintentional transfer of ink from the ribbon onto unprinted areas of the paper or other record media which is adjacent the ribbon during printing operation. This ribbon offset can make character recognition, such as OCR (Optical Character Recognition) or MICR (Magnetic Ink Character Recognition), difficult and sometimes impossible.
The present invention provides a thermal transfer medium in the preferred form of a ribbon which eliminates or substantially reduces ribbon offset during the printing operation.
Representative documentation in the area of nonimpact printing includes U.S. Pat. No. 3,527,666, issued to M. M. Labes on Sept. 8, 1970, which discloses pressure sensitive copying material having a carrier layer impregnated with an image forming material and a transfer layer having a plurality of capillary pores therein for receiving and retaining the image-forming material from the carrier layer at different rates.
U.S. Pat. No. 4,597,793, issued to A. Amon et al. on July 1, 1986, discloses a desensitizing ink for wet offset printing on an acceptor surface of a chemical duplicating set having at least two superimposed sheets, one of the facing surfaces of which has an electrophilic acceptor coating and the other a nucleophilic coating capable of producing a chromogenic reaction to form a fine stable emulsion of water in the ink.
U.S. Pat. No. 4,599,111, issued to A. Amon et al. on July 8, 1986, discloses a desensitizing ink for wet offset printing on an acceptor surface of a chemical duplicating set wherein a nucleophilic alkoxylated compound is bridged as a polyurethane to increase its molecular weight and to improve ink transfer.
U.S. Pat. No. 4,599,260, issued to B. S. Truskolaski et al. on July 8, 1986, discloses a directly printable tape comprising a polymeric film backing having a low adhesive backsize coating on one surface and a pressure-sensitive adhesive on the other surface. The backsize coating is ink imprintable and is low-force removable from the adhesive without transfer of ink thereto.